1. Field of the Invention
The present invention relates to an internal-combustion-engine combustion state detecting apparatus that is capable of detecting abnormal combustion in an internal combustion engine.
2. Description of the Related Art
In recent years, problems of environmental conservation and fuel depletion have been raised, and in the automobile industry, solutions to these problems have also become big issues. As solutions to the foregoing problems, many technologies that intend to raise the efficiency of an engine as much as possible have been developed. However, on the contrary, the occurrence frequency of abnormal combustion has been raised and hence problems such as damage to an engine and deterioration in the durability and merchantability have occurred.
To date, as an apparatus for detecting abnormal combustion in an internal combustion engine, there has been proposed an apparatus that determines that there exists abnormal combustion in the case where the position of the peak cylinder pressure of the internal combustion engine is more advanced than a predetermined crank angle position (for example, refer to Japanese Patent Application Laid-Open No. 2006-46140). In the conventional apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-46140, the detection of the peak position is performed by utilizing an ion current that is obtained by applying a voltage to ions produced due to combustion of an inflammable fuel-air mixture.
In the conventional apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-46140, the peak position of the cylinder inner pressure can be estimated from an ion current; however, because the peak position, of the cylinder inner pressure, which occurs as a result of abnormal combustion is in fact located at a position immediately before or after ignition, and particularly in the case of at a position immediately after the ignition, the peak position is likely to be located in a period of spark discharge caused by ignition, no ion current can be detected during the spark discharge, whereby there has been a problem that the peak position of the cylinder inner pressure cannot be detected.
Even though detection of an ion current can become possible from a timing immediately after ignition, it has been difficult to distinguish an ion current peak timing, represented by a flame angle, which is created through ignition operation, from a cylinder inner pressure peak timing.